1. Field of the Invention
The present invention relates to a coating apparatus and a coating method, and specifically, to a coating apparatus and a coating method capable of performing coating stably in a broad range of coating conditions and inhibiting the occurrence of product failures, and a coating apparatus and a coating method capable of inhibiting the occurrence of product loss at the time of starting coating.
2. Description of the Related Art
A planographic printing plate precursor is manufactured generally by forming a support web by graining at least one surface of an aluminum web made of pure aluminum or aluminum alloy and forming anodic oxide coating on the surface if necessary, and then, by coating the grained surface of the support web with plate-making layer forming liquid such as photosensitive layer forming liquid and heat sensitive layer forming liquid and drying it to form a photosensitive or heat sensitive plate-making surface.
A bar coater is generally used for coating a strip-shaped body such as the support web with the coating liquid such as the plate-making layer forming liquid.
As the bar coater, conventionally, a bar coater has been generally used, which has a bar that rotates in the same direction as or opposite direction to a running direction of the web while being in contact with an under surface of the continuously running web, and a coating part that forms a coating liquid reservoir by discharging coating liquid on the upstream side of the bar in relation to the running direction of the web (hereinafter, referred to as just “upstream side”), and coats the under surface of the web with the coating liquid at the time of running of the web.
As the bar coater, a bar coater (Japanese Utility Model Registration No. 2,054,836) has been generally used, which has a first sheathing board provided close to the bar on the upstream side of the bar and formed so that the thickness of the upper end thereof is thinner toward the downstream side in relation to the running direction of the web (hereinafter, referred to as just “downstream side”), the upper end of the first sheathing board being bent toward the bar, and a flat surface having a length of 0.1 to 1 mm on the top thereof. A bar coater (Japanese Patent Application Publication (JP-B) No. 58-004589) has been also used, which has a first sheathing board formed so that the thickness of the upper end thereof is thinner toward the downstream side, a bar, and a second sheathing board provided on the downstream side of the bar.
However, when the running speed of the support web is increased, an entrained air film as a film of air running while accompanying the support web, i.e., entrained air tends to be formed on the surface of the support web.
In both of the bar coaters, there is a problem that, when the entrained air film is formed on the surface of the support web, since the entrained air film is introduced into the coating liquid reservoir, the coating liquid becomes prevented from being deposited uniformly on the surface of the support web, and thereby, defects such as breakage of the film occur to cause unstable coating of the coating liquid.
As a bar coater capable of solving the problem, a bar coater is conceivable, which has a primary bar disposed on the upstream side along the carrying direction of the support web, a secondary bar disposed on the downstream side of the primary bar, and a between-bars liquid reservoir disposed between the primary bar and the secondary bar.
By the bar coater, the problem that various kinds of defects due to the entrained air occur when the carrying speed is high may be solved.
However, even in the bar coater, in the case where the relationship between a coating amount of the coating liquid at the primary bar and a deposit amount of the coating liquid after the strip-shaped body passed through the secondary bar is unsuitable, a problem that a liquid reservoir uniform along the width direction of the support web can not be formed in the between-bars liquid reservoir can also arise. In addition, when the coating amount is too excessive relative to the deposit amount, the liquid reservoir may fluctuate in the width direction of the support web to produce a streak defect, etc.
Further, even in the bar coater, when the coating conditions such as a composition and a supplied amount of the coating liquid and the carrying speed of the web are within a specific range, the coating amount of the plate-making layer forming liquid is not controlled at a constant amount at the time of starting coating, quality failures such as thick coating and bubble streaks can be produced.
As means for preventing the quality failures, a method for setting the number of rotations of the primary bar at the time of starting coating to the lower speed than the normal speed, and a method for inhibiting the occurrence of the thick coating and bubble streaks by setting a smaller amount of coating at the time of starting coating, are conceivable.
However, in the case where those methods are adopted, at the part where the primary bar is rotated at low speed and the part where the coating amount of the coating liquid is small in the planographic printing plate precursor as a product, the product loss increases and the manufacturing cost rises.
The invention is achieved in order to solve the above described problems, and an object thereof is to provide a coating apparatus and a coating method capable of performing coating stably in a broad range of coating conditions and inhibiting the occurrence of the product failures.
In addition, another object of the invention is to provide a bar coater and a coating method capable of inhibiting the occurrence of the product loss at the time of starting coating and cutting back on the coating cost.